Thanks for posting this, Sewbizgirl and also FelineFanatic about it traveling up the needle bar. It made a light bulb go off in my head. Every now and then I get threadlock problems in my embroidery machine, and it's common to use spray baste for that. It's part of many instructions for projects. What I now think is happening is that the gunk above the needle snags thread and when it recoils up above it gets caught. I'm definitely going to be taking preventive action. Never know what useful stuff I might pick up on this board, and I'm grateful to all who share information and advice!
BTW, for quilting I've mostly weaned myself off the spray. I really like the method with long pins and ear plugs. Spray is expensive and I worry about prolonged exposure.